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Gary LaPook writes:

You should also check the files section of the Yahoo sextant group for
more information on sextants.

http://groups.yahoo.com/group/Sextants/files/

gl

On Apr 30, 7:27 pm, Bruce  wrote:
> Greetings to all list members.  I have been enjoying the list and
> archives for a month or so.  I am in the process of continuing to
> re-learn celestial navigation after a 25 year break.  I began to learn
> the art years ago in a Canadian Merchant Officer college, but did not
> finish the program.  At the time, we navigation cadets were very
> reluctant to use the antiquated methods that were being taught to us, as
> we ground through the lessons using "Norie's Stories".
>
> Now, I am in the process of acquiring a new copy as my original seems to
> have drifted away. I know that I will eventually succumb to the siren
> call of my scientific calculator, or heaven forbid, a starpilot, but I
> still want to wake up those brain cells that once knew how to use log
> tables.  On a side note. I was formally taught how to use the slide rule
> in high school too.  I saw my first GPS when I was a second year cadet.
> It was on the bridge of a French bulk carrier that we were loading
> directly into, from our self-unloader, in Sept Iles bay. The thing was
> the size of a small desk. I was on a coastal ship and we only had
> loran-c. RDF and radar.We didn't even carry a sextant, but the old man
> made me box the compass. Yikes!
>
> Presently, I have a spanking new copy of Geoffery Kolbe's  /Long Term
> Almanac, /and John Karl's/ Celestial Navigation in a GPS Age. / I was
> inspired by Geoffery's stories of navigation in the Sahara.  I did not
> even realize that air craft sextants existed, and I am looking for an
> A-12 as it would allow me to easily take sites without finding a
> horizon.  I am also considering a used theodolite too, but I have found
> the old mechanical ones still cost a fortune as they are reliable and
> much in demand by surveyors in the remote Canadian wilderness.  I am
> also fascinated by the Lunar Distance methods, so a naval sextant will
> have to be a part of my kit, eventually.
>
> Anyway, that is my rambling introduction, but I have a few questions for
> the list.
>
> 1)Sextants are expensive precise instruments, but they are still made of
> brass and aluminum. Why does no one use invar to make them more
> resistant to thermal expansion?
>
> 2) It is supposed to be possible to get exact GMT by observing the moons
> of Jupiter, but I have yet to find any tables that have more than a
> minute accuracy.  Has anyone else tried and had better luck?
>
> 3) I have looked, and bid on, several a-12 air sextants on e-bay. Has
> anyone ever had a good result with an e-bay A-12?  Are they fairly
> rugged? I hate buying a pig in a poke, but celestaire is not cheap (like
> me).
>
> 4)I have heard that it is possible to modify am A-12 to see the horizon
> by inserting a prism somewhere. Has anyone done it, and can it be done
> so that the bubble can still be used.
>
> Here is a very old Norie's 
online.http://books.google.com/books?id=OzwEAAAAQAAJ&printsec=frontcover&dq=...
>
> Thank You
>
> Bruce Hamilton
> Vancouver, BC, Canada
>
> bruce.hamilton    (antispam you know what goes here) shaw.ca
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